Panelists performed blind quantitative descriptive analysis using a standard list of descriptors including six odor (overall oaky, fruity, sawdust, vanilla, toasty, spicy) and five taste descriptors (acidity, bitterness, tannic intensity, structure, length). The sensory sessions were organized by series with the same wine aged in fire-bent and immersion/fire-bent barrels. The order of presentation was arbitrary and different for different panelists to obtain more objective data.

The tasting sessions were conducted in tasting rooms following the usual practices in wine tasting and were conducted by a session observer. Before the sensory analysis, the bottle was tasted in order to look for possible off-flavors and was rejected if there was an abnormal odor.

Panel members awarded 0 to 10 points according to the intensity of each descriptor (0 – very weak, 10 – very strong).

The values given by each taster were normalized using the average value for that taster over the entire series. The Independent Student’s T-test was applied to the normalized values to identify the descriptors for which there was a variation in intensity between the barrels made using “immersion” and the “traditional process.”

Only those descriptors showing differences with a probability below 5% were retained for further processing.

Analysis of volatile compounds

The following 19 odoriferous volatile molecules from oak wood were assayed in the wines using GC-MS:3

Wines aged in barrels where the staves have been bent following
hot water immersion are empirically perceived to be less marked
by oaky aromas. However, to date, very little scientific data was
available concerning the impact of this bending technique on wood/wine
exchanges, thus making it impossible to explain the sensory differences
noted in empirical observations.

This report presents the results of a two-year comparative study
of the two stave bending techniques, focusing on the sensory profiles
of wines aged in the different types of barrels and their concentrations
of volatile molecules.

Material and methods

Barrel production

The barrels were made by Tonnellerie Seguin Moreau (Seguin Moreau
Burgundy ZAC du Pré Fleury les Creusottes Nord, Chagny, France)
using staves bent either following immersion or by heating over a
fire (see Figure 1). All barrels were produced from one batch of
French fine grain oak.

In the “traditional process,” raised barrels are preheated (A) for
10 to 15 minutes to a temperature of 100° to 120°C to soften the wood
fibers and make them pliable. This process does not cause any major
production of compounds arising from toasting; indeed,

any modifications
are insignificant compared to those that occur during the toasting stage.

In the process employing bending by “immersion,” the preheating stage (A) is replaced by soaking in hot water (B). The temperature of the water does not exceed 100°C; production of toasting products due to heating are negligible.

Toasting – The heating process that causes chemical modifications in the wood was performed according to the standard “medium-long” protocol used in the cooperage. This stage was identical, irrespective of the type of bending process: heating over a fire or by immersion.

Wines

Trials occurred on nine sites with nine wines (three white wines and six red wines) from two different vintages: 2007/2008 (Table I). Wines were either barrel-fermented or put into barrel before or after malolactic fermentation. There were three barrels in each wine lot.

Sensory analysis

Sensory analysis by a tasting panel of Seguin Moreau staff (panel I of 8 to 14 persons), and a trained panel of enology students from the Institut Universitaire de la Vigne et du Vin (panel II of 16 to 18 persons), was done at regular intervals, as described in Table I.